1) Field of the Invention
This invention relates to a transverse flux electrical machine, that can be used as an alternator or a motor, and that is intended to be used for the conversion of a rotary movement into electrical power, and vice versa.
2) Description of the Prior Art
Transverse flux electrical machines include a circular stator and a circular rotor, which are separated by an air space called an air gap, that allows free rotation of the rotor with respect to the stator, and wherein the stator comprises soft iron cores, that direct the magnetic flux in a direction that is mainly perpendicular to the direction of rotation of the rotor. The stator of transverse flux electrical machines also comprises electrical conductors, defining a toroid which is coiled in a direction that is parallel to the direction of rotation of the machine. In this type of machine, the rotor comprises a plurality of identical permanent magnet parts, which are arranged so as to create an alternate magnetic flux in the direction of the air gap. This magnetic flux goes through the air gap with a radial orientation and penetrates the soft iron cores of the stator, which direct this magnetic flux around the electrical conductors.
Certain transverse flux electrical machines include a stator which comprises horseshoe shaped soft iron cores that are oriented in such a manner that the magnetic flux that circulates inside these cores is directed in a direction that is mainly perpendicular to the direction of rotation of the rotor.
The perpendicular orientation of the magnetic flux in the cores of the stator, with respect to the rotation direction, provides a pole pitch typically lower than 20 mm, which gives to transverse flux electrical machines a high ratio of mechanical torque per weight unit of the electrical machine.
In the prior art, the horseshoe shaped soft iron cores are monolithic. Consequently, the horseshoe shaped soft iron cores are opened, i.e. the two ends of the horseshoe are sufficiently remote from one another that the stator coil may be inserted therebetween.
Also, in the prior art, the horseshoe shaped soft iron cores are monolithic and may entirely consist of piled up metal sheets. In this case, it is not possible to machine the stator to ensure its circle symmetry, without short-circuiting the metal sheets with one another. A non-machined stator increases the inaccuracy of the thickness of the air gap between the stator and the rotor. Also, in the case where the horseshoe shaped soft iron cores are made of identical piled up metal sheets, additional magnetic losses are produced inside the horseshoe shaped soft iron cores in the region that is located close to the air gap, the reason being the circumferential component of the magnetic induction B that is produced by the rotor. This circumferential component of the magnetic induction circulates perpendicularly to the plane of the metal sheets constituting the horseshoe shaped soft iron cores and alternates with a frequency that is equal to the electrical frequency of the machine, which generates eddy current losses in the metal sheets.
In the prior art, the horseshoe shaped soft iron cores are monolithic and may be entirely made of a magnetic material that is compacted under high pressure. In this case, the electrical machine thus constituted will result in reduced power efficiency, nominal torque and mechanical tolerance to vibrations, and shocks. Reduction of performances is associated with the presence of a compacted magnetic material whose magnetic permeability, magnetic induction at saturation and mechanical breaking strength are lower than those of the magnetic metal sheets, and whose eddy current losses are more important than those of magnetic metal sheets.